Was he really the abuser from her childhood?
At first, I was convinced he wasn't. I thought that if he truly were her rapist, she would have recognised him (while the interrogator is an excellent actor who can fake voices, some truly traumatic things just aren't easily forgotten); also, that he would have started taunting her about her past much sooner in order to break her more effectively. As it is, he never mentioned the horrors of her childhood until she spoke of it first, and it looked like he got the idea to impersonate the abuser purely from the information she had given him; it could be his last resort to break her. So when she addressed the man in the end, I assumed she was speaking to the abuser through the interrogator, that the interrogator's character had kind of dissolved, and she was addressing both the abuser and the government.
Come to think of it, however, I now believe he really was the abuser in question. At the time when the interrogation was taking place, "Closet Land" hadn't yet been published, so the government couldn't know the booklet might be "politically incorrect"... unless they'd been spying on her for a long time. And why would they spy on a harmless author who wrote about flying cows and cats with wings? The interrogator himself admitted that those stories were inocuous. This leads me to presume that the whole thing was the interrogator's initiative--perhaps he thought this out the moment when she told her mother, "you never noticed." His desire to have her "removed" would explain his obstinate effort to make her sign the confession even though he knew perfectly well she had had nothing to do with politics.
So now my question is, why was he so desperate to have her convinced? It's not like she had told on him--she had just "coded" the message into a harmless book, and no reader could guess it had something to do with him. Was he alarmed by the fact that she had dared confess to her readers even in such veiled terms? Or, as the victim suggested, was it really a revenge on his part: revenge because she'd escaped from him into her imaginary world? If so, his cruelty really knows no boundaries.